Ecotoxicology and Climate
Edited by P. Bourdeau, J. A. Haines, W. Klein and C. R. Krishna Murti
@ 1989 SCOPE. Published by John Wiley & Sons Ltd
2.1
Climates of the World Seen
from an Ecotoxicological Perspective
G. A. McKAYANDM. K. THOMAS
2.1.1
INTRODUCTION
The influence of weather on the environment is very apparent in growth
processes, which are controlled by the availability of light, heat, and water.
However, climate and weather are a continuum and climate is often defined
as the sum of weather. It is an integral part of the natural environment, and
is recognized as a major biological control. The effects of climate are evident
in occurrences of skin cancer and the extent of biomes. From a toxicological
viewpoint, interest in climate usually is focused on the atmosphere's ability to
influence the toxicity of pollutants as well as their dispersal and transport.
Study of climate information reveals the nature of commonly experienced
weather as well as extremes and the risk of occurrence of harmful combinations
of climatic elements. As a rule these characteristics are relatively conservative
over large areas. However, climatic regions or zones display many anomalous
features on the meso and micro scales, i.e. climates that differ from the regional
average because of special terrain or relatively local effects of the atmosphere.
For example, the Los Angeles smog results from geography, a relatively unique
combination of atmospheric processes and a cold offshore ocean current.
Similarly valley climates differ noticeably from those nearby at higher elevation.
Over the globe there are many different climatic regions, the number being
defined by whatever classification system is employed. Broadly speaking, the
climatic differences exist because of differences in geography, the latitudinal
variation in the energy from the sun, the availability of moisture, and the
influence of these factors on atmospheric dynamics. These differing climates
have contributed to the creation of ecosystems and in turn are influenced by
the vegetative cover. The differences are manifest in the major biomes of the
earth: tropical rain forests, deserts, grasslands, boreal forests, etc. This chapter
focuses on the large-scale characteristics of climate that identify with these
features, and to a lesser degree on atmospheric processes that relate to pollution
concentrations, transport,and performancewithin climaticzones.
15
16
Ecotoxicology and Climate
2.1.2 THE ATMOSPHERE
The atmosphere can be considered as consisting of horizontal layers. Adjacent
to the earth lies the troposphere, which contains the bulk of the atmospheric
mass and which extends vertically to about 10 km in mid-latitudes and to 20 km
near the equator. It contains the planetary boundary layer within which occurs
an active exchange of heat, water vapour, and contaminants between the oceans
and land surfaces. Above the troposphere lies the stratosphere, which extends
to a height of above 82 km. Within the stratosphere is the ozone shield, which
is vulnerable to the catalytic effects of dissociated chlorofluorocarbons.
The tropospheric wind system is highly organized, being controlled primarily
by the earth's rotation and differential heating by the sun. Tropospheric winds
generally increase with height. At the equator are found the relatively calm
doldrums. Poleward of the doldrums the trade winds exist, and then the horse
latitudes, a region of light winds near 30° latitude. Seasonal changes in the
relative warmth of the ocean and land areas results in monsoons; these are
pronounced in tropical and subtropical areas. Farther poleward, roughly between
30° and 60° , are stormy regions within which the winds blow mainly from the
west. At high latitudes the winds tend to be weaker and more variable. Many
departures from these generalizations are found, both seasonally and annually.
The departures are extremely important since they are often responsible for the
exchange of pollutants between zones, exposure to more critical levels of
pollutants, and the occurrence of anomalous climatic environments at ground
levels. Synoptic-scale analyses provide insight into their character.
The vertical movement of air is of great importance in the initial lifting,
diffusion, deposition, and transport of pollutants. Large-scale ascending motions
occur over mountains, weather fronts, active low-pressure areas, and in
equatorial regions; however, smaller-scale turbulence and convection are of
greater relevance in the vertical movement of pollutants. Turbulence induced
by frictional drag and convection is the cause of the earth's boundary layer.
Well-mixed, the layer has a depth of 1-3 km, varying diurnally and seasonally
with the stability of the air, the roughness of the ground, and wind velocity.
Land, sea, and other topographically controlled breezes or drainage of air occur
within the boundary layer. Strong convection lifts air from the lower to the
faster-flowing middle and high regions of the troposphere, and at times into
the stratosphere. Strong convection is found daily over the tropical land areas,
but elsewhere it is infrequent and the exchange of air between the troposphere
and stratosphere is slow.
Horizontal tropospheric circulations are strongest in mid-latitudes and at times
are concentrated into 'jet streams'. Best known is the polar jet stream, found
at about 7 km height and within which winds may be in excess of 250 knots.
Highly variable in character, it may be sinuous or more commonly move from
west to east. The subtropical jet, found at about 28° latitude and at a height
Climates of the World Seen from an Ecotoxicological Perspective
17
of 10 km, has maximum winds between 100 and 150 knots. Other jets are found
at both high and low levels, for example the tropical easterly jet that moves
from West Africa to the Caribbean.
The capacity of the winds to transport pollutants varies with the wind field.
Those confined to the boundary layer have relatively short residence times and
their depositions tends to be local. Exceptions occur particularly at higher
latitudes where ducting is more common. Convection lifts contaminants to
stronger wind-levels where they can be transported over thousands of kilometres
within short time spans. For example, dense smoke from western Canada forest
fires in 1950 was jetted across the North Atlantic in a day.
The somewhat zonal, relatively uniform fields of wind, along with temperature,
water vapour, and radiation, are the bases of the world's climatic zones. Within
the zones conditions, both at the surface and in the upper air, tend to be relatively
conservative, such that general statements can be made as to how they distribute
and influence the performance of contaminants.
2.1.3
CLIMATE AND ATMOSPHERIC CONTAMINANTS
The atmosphere acts primarily as a conduit by which pollutants are conveyed
from a source to an ecosystem. It may also playa role in photochemical change
that alters the toxicity to the emitted substances. Furthermore the behaviour
of the toxics can be influenced by climatic conditions, and the pollutant acting
alone or in combination might be instrumental in altering the nature of the
climate.
Toxics released into the biosphere can move along a variety of pathways, for
example by streamflow into oceans, by food chains, and by the atmosphere
to be deposited on the land or on water surfaces. The atmosphere is a major
pathway that can be used at different stages in this process. For example, the
atmospheric PCB contribution to Lake Superior is estimated to be 6600-8300 kg/
year, five to seven times the direct input by industry or tributary streams (Bruce,
1983). 'Re-emission' of toxics, i.e. a secondary release of already transported
contaminants, allows them to be transported still farther from their original
source (attar, 1979). The effectiveness of these processes within a zone relates
to the fundamental nature of the climate (winds, stability, etc.) of the zone,
which must be appreciated to understand the role of climate in the dispersal
of toxics, and to the nature of the pollutant.
Gases that are relatively inert remain unchanged for long periods of time and
become widely diffused throughout the atmosphere. Carbon dioxide background
levels, for example, are similar from pole to pole, although seasonal and regional
differences occur. More active gases, such as sulphur dioxide and oxides of
nitrogen, enter readily into chemical reactions and, therefore, have a shorter
residence time. For that reason they are more variable in their global and regional
distribution. The same holds true for carbon monoxide. Thus while the stable
18
Ecotoxicology and Climate
gases create effects that are generally global.the reactivegases are best considered
in the context of zonal climates.
Pollutants are removed from the atmosphere most effectively by precipitation.
Precipitation cleanses the atmosphere, but in doing so, it can deposit large
amounts of pollutants over specific areas. Droplets of about 2 mm diameter
are theoretically the best collectors, so that even a very light rainfall or drizzle
can deposit large quantities. Dry deposition is much slower but it, too, can be
quite significant. The subsequent dissolution of the particulates by rainfall may
result in relatively strong chemical concentrations in runoff and on vegetation.
In the case of melting snow cover, both the dry and wet deposition chemicals
are leached from the snow in the early stages of melting, thereby producing
the phenomenon of 'acid shock'.
Variations in climate can severely damage existing ecosystems and may lead
to the introduction of others that are highly vulnerable. The warm decade of
the 1930s enabled the introduction into sub-Arctic regions of many new crops
that could not survive the colder years that followed. Climate variations are
marked in the semi-arid transition zones, such as the Sahel, where ecosystems
may alter greatly from year to year. Low temperatures reduce metabolic
processes and thereby may reduce impacts on biota. On the other hand the
anomalously cold winter of 1976-77 in North America did major damage to
coastal marine ecosystems. Different seasons also introduce their peculiar
problems. The turbulent floods that arise with the onset of a rainy season may
produce soil erosion and stir up toxin-bearing river bed sediments. Seasonal
droughts may reduce surface water volumes and thereby increase the pollutant
concentration, as well as raise the water temperature. Climate variations, such
as drought, may act to predispose to, or incite damage within, ecosystems that
are threatened by toxins. Allergens, dust storms, monsoonal rains, and the
temperature/humidity combinations that favour the explosive development of
rusts or blights all have a seasonal character. By examining the anomalous
episodes, seasonal shifts, longer-term variations, and other characteristics of
climate, much can be learned of climate-related hazards.
2.1.4
CLIMATE ZONATION
The Sahara, boreal forest, and the tundra conjure up impressions of vast regions
with relatively unique, but uniform climates. Many attempts have been made
to classify the Earth's climates to obtain a brief comprehensive appreciation
of their characteristics, similarities and differences. Early classifications, such
as that of Koeppen (Koeppen and Geiger, 1935), are based largely on values
inferred from vegetative cover. More recent systems have introduced spatial
and temporal variability using statistics and features such as ecoclimate,
topoclimate, microclimate, and mesoclimate, etc. to introduce different scales
of interest.
Climates of the World Seen from an Ecotoxicological Perspective
19
Global zonation, of necessity, must be highly generalized and concentrate
on the major differences as indicated by temperature and moisture as well as
their patterns across the continents. However, a too generalized classification
scheme will not reveal ecologically important phenomena that occur on fine
scales of time and space. For example, specific incidents of episodic stagnation
or specific trajectories of pollutants will not be revealed by highly generalized
zonation techniques. Nevertheless many processes of importance to the
ecosystem must and can be inferred from the zonal characteristics. Occurrences
such as periods of stagnation tend to be repetitive, and their frequency, extent,
and intensity as well as the nature of extreme incidents may be revealed by
reference to climate statistics for representative locations within a zone.
The zonal boundaries and characters are coarse averages and they may shift
briefly or for longer intervals of time. Such upsets are often associated with
the displacement of weather fronts and monsoonal systems from their mean
position. The result usually is widespread regional droughts as well as areas of
moisture excess and anomalous heat and cold. A semi-arid region may become
arid or subhumid during a climate fluctuation. The El Nino/Southern Oscillation
phenomenon that occurs every 2 to 7 years is commonly associated with regional
climatic fluctuations in tropical areas, for example torrential rains in Ecuador,
and drought in northeast Brazil, the Sahel, and southeast Asia in 1982-83. In
arid areas most variability is interannual, but dry episodes that span several
growing seasons and sequences of dry episodes may occur-a climate feature
that is recurrent in the Sahel.
Five generalized zones are identified. These are: (1) Equatorial-where
the
climate is hot and moist all or during the larger part of the year; (2) Desert/
Steppe-where water supply is insufficient to meet growth potential; the zone
is generally hot all year but with a cold season at higher latitudes; (3) MidLatitude-a
somewhat humid, variable climate; (4) Boreal/Taiga-a
region
with a short growing season and cold winters; and (5) Tundra/Ice-cap-a
zone
where mean temperatures are below freezing for most of the year and precipitation
is generally light. These five zones are delineated on the accompanying map
(Figure 2.1.1) and their relevant characteristics are specified in the zonal narrative
that follows.
Not identified are the climates of oceanic areas, and these cover 710,10of the
earth's surface. Oceanic climates strongly reflect the nature of the ocean surface,
as well as the characteristics of the air masses that traverse it. Precipitation is
pronounced in areas of atmospheric convergence, such as along the intertropical
Convergence Zone (ITCZ), and in those areas swept by the major west-to-east
moving mid-latitude storms. Also worthy of note are the highland climates,
such as are found in East Africa, Tibet, and Ecuador. Altitude strongly
influences climate and the climates of highlands in any general zone are
anomalous. The normal lapse rate of temperature with height is about - 6°C
per 1000m, but thereareimportant exceptions.Precipitationand fog occurrences
N
0
LEGEND:
1. Equatorial
2. Desert/Steppe
3. Mid-Latitude
4. Boreal/Taiga
5. Tundra/Icecaps
6. Highland --.I
I
Figure 2.1.1
Major climate zones for the world's land areas
Climates of the World Seen from an Ecotoxicological Perspective
21
generally increased with height along a windward slope, and snowfall is general
whenever precipitation occurs and air temperatures are sub-zero., Pronounced
orographic precipitation can purge large volumes of pollutants from the
atmosphere, as along the southwestern coast of Norway. Mountain ranges act
as barriers to the inflow of moisture so that downwind regions, particularly
valleys and sheltered slopes, are relatively arid. Highland climates typically are
subject to large diurnal fluctuations in temperature and night frosts.
2.1.5
EQUATORIAL ZONE
This hot moist zone covers most of Central America, the Caribbean, Brazil,
and the central core of Africa from Senegal eastward through Nigeria and Zaire
to Mozambique and Madagascar. Most of India, Burma, and the remainder
of southeast Asia along with Indonesia and northern Australia also belong in
this zone. Tropical rain forest covers the core. Grassland-savannah on the
poleward edges experiences both wet and dry seasons.
A major feature of the poleward side of the zone is the monsoon. That of
India and southeast Asia is best known. There the wet monsoon arrives in
summer from the southwest, and the dry monsoon occurs as winds blow outward
from the continent. The onset of rain is strongly marked and the impact on
the environment is spectacular. Other regions experiencing pronounced
monsoons include Central Africa, the Philippines and Northern Australia. The
summer monsoon in West Africa is wet, but both of the East African monsoons
are dry. The depth of penetration inland is variable. Delays in onset or failure
of the wet monsoon can have devastating effects on agriculture and water
resources.
Mean daily temperatures for the zone range from 20 to 26°C. Absolute
extremes are rarely above 37°C or below 15°C. The diurnal range may be as
high as WOC, but the annual range from the coldest to the warmest month is
usually less than 3°C. Copious dew occurs at night under clear skies.
Precipitation is heavy, usually about 2500 mm a year. Most falls from afternoon
thunderstorms that are of short duration and high intensity. Hurricanes account
for much of the autumnal rainfall on coastal areas at higher latitudes. Heaviest
annual rainfall occurs where the trade winds impinge on mountain ranges. The
core area has no dry season, but short-duration droughts occur because of the
high rates of evaporation and transpiration. On both polar limits of the zone
there is a definite dry season with little or no precipitation. Seasonal rainfall
there is more variable and both unseasonal droughts and floods may occur with
the occasional anomalous displacement of the ITCZ.
Cyclonic storms are few, but hurricanes or typhoons and tropical storms
spawned over oceanic areas can devastate island and coastal areas. Examples
are provided by the widespread loss of life and flooding off the Bay of Bengal
in 1970and againin 1985.On the other hand hurricanesprovideareas of Mexico
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Climates of the World Seen from an Ecotoxicological Perspective
23
with water that is urgently needed for agriculture. The storms are most frequent
in the northern hemisphere, approaching the southeast coasts of Asia and North
America in late summer and autumn. Within the southern hemisphere the north
coast of Australia and southeast Africa are most vulnerable. They quickly lose
their strength inland, but the moist winds can feed rainstorms far inland.
Convection is pronounced by day, due to the strong insolation, and the
atmosphere is mixed to great heights. The strong convection and intense, almost
daily, precipitation along with low levels of fossil fuel combustion maintain
relatively good air quality. Recognized sources of pollution are agricultural areas,
due to the burning of the trash cover and the use of pesticides, and industrial
areas. The erosive power of the rainfall is great and this may contribute to the
pollution of water courses and lakes.
2.1.6
DESERT/STEPPE
ZONE
The extent of this zone is depicted in Figure 2.1.2, which shows the distribution
of arid land over the world (United Nations, 1977). Generally speaking, there
are two arid belts around the globe somewhat aligned along the tropics of
Capricorn and Cancer (there are notable exceptions). The major deserts are
found in both North and South Africa, Arabia, south-central Asia, and
Australia. The main areas of steppe climate are found between latitudes 35°
and 50° in both hemispheres, but primarily in Asia, western North America,
southwestern Africa, and South America.
Dry climates occur where the demand for water (for evaporation and transpiration) exceeds the supply (precipitation). Within this zone the temperature
conditions are favourable but precipitation is limiting to growth. Because of
the seasonal nature of the precipitation, growth, if it occurs, is seasonal. The
temperature range is large. Even warmer conditions than are found in the
Equatorial Zone occur at low latitudes, and quite cold temperatures occur in the
continental interiors at high latitudes. In the Sahara the surface layer of the soil
reaches 30°C in winter and as high as 70°C in summer at midday. The average
relative humidity is about 10070,dropping at times to as low as 2%. With low
humidity and often bare ground, daily air temperature ranges as great as 18°C
occur. There is little rainfall over deserts and steppes and adjacent oceanic areas.
Precipitation is erratic and highly localized. Over the steppes it occurs in winter
in the north and in summer in the south. Over the deserts it is brief, missing
in many years, and there is no seasonality. Thunderstorms are the major source
in the tropics, and in some areas storms along the ITCZ provide seasonality
to the precipitation. ITCZ storms provide precipitation between East Africa's
two dry monsoons. Mid-latitude storms are usually the cause of winter
precipitation in poleward regions. Over the steppes precipitation totals
sometimes exceed 750 mm a year, but because of its seasonal nature and
the hot demanding temperatures, aridity is the dominant characteristic.
24
Ecotoxic%gy
and Climate
Except for the small core areas, there are marked seasonal changes in climate
within this zone. For example, in the northern hemisphere, the tropical rainy
zone migrates into the southern edge of the dry zone in summer, and winter
storms bring precipitation to the northern margins in that season. Convection
is vigorous by day in the summer but limited by large-scale atmospheric stability.
Winds tend to be light except in the northern margin in winter. There is little
rain to scavenge atmospheric pollutants. Strong nocturnal temperature inversions
and the highly stable air masses that form along coasts having cold water
offshore, favour the concentration of emitted pollutants. Coastal fog, drizzle,
and low temperatures reduce the soil water deficiency and favour vegetative
growth along the western coasts of continents. The zone is not highly
industrialized so that there are few concentrated sources of atmospheric
pollution. However, where they exist there can be serious pollution problems,
as in Cairo, Mexico City, and newly urbanizing areas that are located in
topographic basins.
2.1.7
MID-LATITUDE ZONE
This zone includes areas in North America along the Pacific Coast, eastern
United States and southeastern Canada, Western Europe extending into central
USSR, and eastern USSR, China, and Japan. It also includes parts of central
Peru and northern Chile, parts of eastern South America between 20° and 35°S,
New Zealand, and parts of coastal South Africa and southern and eastern
Australia. In a sense the climate of this zone is heterogeneous. It is most readily
identifiable by what it is not. It is not tropical, arid, or frigid, but rather
transitional between these types and at times displays some of the characteristics
of each.
The zone exhibits a seasonal rhythm from cold winters to warm summers,
and marked seasonal and interannual variations in precipitation. Summers have
relatively stable weather with somewhat tropical conditions existing where the
circulation is off warm oceanic areas. In the northern hemisphere, mean monthly
temperatures in summer are about 27°C in the south and 20°C in the north,
and daily extremes about 35°C. The incursions of cold air in winter result in
large annual ranges of temperature, which reach 38°C at Winnipegand 29°C
at Moscow. Winter storms are numerous as cold and warm air masses alternate
in the south, the cold dominating in the north. Coastal areas have most of their
precipitation in the winter months, while interior continental areas have the most
precipitation in the summer. Snowfall contributes a significant portion of annual
precipitation totals, which average over 2500 mm in the rainiest maritime areas
and less than 500 mm in the more continental areas. Snow cover may persist
on the ground 3-5 months of the year in the more poleward areas. In maritime
areas many locations have over 150days a year with precipitation; Bahia, Chile,
averages 325 precipitation days because of its oceanic exposure.
Climates of the World Seen from an Ecotoxicological Perspective
25
With the seasons the ground cover changes from green grassland and forest
throughout the summer, to dead, brown, or leafless vegetation in winter, with
snow cover for appreciable periods on the poleward side. Evaporation and
transpiration demand exceeds precipitation in summer, but ample winter
precipitation compensates for most deficiencies. Extended droughts occur, but
they are generally of lesser consequence than in more arid regions. There is only
a slight risk of ground frost on the equatorial side of the zone (except at high
altitudes), but the incidence of frost increases poleward so that frost is likely
on 270 days of the year near the poleward limits.
Ventilation is generally good but there are notable periods of stagnation.
Prevailing winds and air-mass stability have led to extensive regional deposition
of pollutants. Stagnation high pressure systems are most common in the spring
and autumn, and their effects are most pronounced in long nights of autumn,
especially in valley locations. Convection is more pronounced in summer; mixing
is effective generally to a height of about 1000m in winter and 1500m in summer.
Four-fifths of the world's fossil fuel consumption occurs within this zone.
Frequent storms both transport emitted pollutants over long distances and
provide effective precipitation scavenging mechanisms. Depositions are heaviest
near and downwind of the major cities and concentrations of industry. Even
longer pathways, from Australia and Asia to South America, are suggested for
traces of pesticides recently found off the cost of Peru (Bruce, 1983).
2.1.8
BOREAL/TAIGA ZONE
This zone hosts the major boreal and 'scrub' subarctic forests of the world.
The boreal/taiga forests extend from Alaska to Newfoundland in North America
and in Eurasia from Norway across northern USSR to the Kamchatka Peninsula.
Boreal forests also exist in alpine areas of other zones, but the forest is virtually
absent from the southern hemisphere for want of land areas within favouring
latitudes.
Winter is the dominant season. The annual range of temperature is typically
about 30°C in the most continental locations. At Yakutsk, USSR, the mean
monthly temperature ranges from 20°C in July to -43°C in January. Winter
temperatures are extremely cold, sometimes colder than in the more polar
regions. Record low temperatures of -68°C were measured at Verkhoyansk
and Oimekon, USSR, and the difference between the lowest and highest recorded
temperatures at Verkhoyansk is 102°C. During the short summer season mean
air temperatures are conducive to growth, which is also favoured by very long
day length. Summer droughts occur, while winter temperatures may fall below
- 30°C for weeks at a time. Diurnal temperature ranges average about 10-15 Co,
and inland the temperature rises occasionally on summer days to above 30°C.
The frost-free season inland ranges from 50 to 90 days, and there is risk of
frost in all months.
26
Ecotoxicology and Climate
Storms are infrequent in summer, and the weatheris frequently clearand
void of haze. Precipitation is light compared to that in mid-latitudes, and about
one-third falls as snow. Convective showers provide the greater portion of
summer precipitation, which ranges usually from 200 to 500 mm. Annual
precipitation ranges from over 1000mm in maritime areas to less than 250 mm
at inland higher-latitude locations. Snow may fall in any month and persistent
snow cover is present from early November to early May. The average duration
of snow cover is about 120 days near the temperature limit, and up to 240 days
near the poleward limit. Maximum depths occur in February and March.
The long winter season, snow cover, and relatively low storm frequency /
intensity make the atmosphere in this zone less effective in purging itself of
pollutants than the Mid-Latitude Zone. The zone receives a net poleward
advection of pollutants from mid-latitudes and this is exacerbated by the
encroachment of industry and urban development along its southern frontier.
Acid deposition is highly episodic, the zone being frequented by storms, periods
of stagnation, and drought as occur in the Mid-Latitude Zone.
2.1.9
TUNDRA/ICE-CAP
ZONE
This zone is found in both hemispheres poleward of 68° , but tundra also occurs
along coasts where sea ice prevails into the summer or where the ocean
temperatures are below 10°C. In the absence of permanent ice the average
monthly temperature rises above freezing for a few months of the year, and
the temperature of the warmest month averages about lOOC.Winter temperatures
average between - 30°C and - 45°C, not as severe as those found in the
Boreal/Taiga Zone because of the moderating influence of the oceans.
Within this zone frost and snow occur in every month and snow covers the
ground for about 10 months of the year. Annual precipitation is generally less
than 350 mm and is primarily due to cyclonic storms. Areas of shallow snow
cover are underlaid by permafrost, and growth occurs mainly in favoured
microclimates. Snow is dry and powdery and quite variable in depth. It averages
30 cm depth inland, but a vast portion of the barren lands in arctic Canada
accumulate relatively little snow cover and may be called a polar desert. The
snow depths increase towards sea coasts and reach about 300 cm on exposed
mountain slopes. Ice disappears but briefly in summer arctic lakes and along
many coasts.
Within the ice-cap area no month of the year has mean temperatures above
freezing. The mean annual range is about 20-35°C, being largest in the interior:
there is no significant diurnal range of temperature. Lowest temperatures occur
at the end of the dark period. The lowest mean annual temperature for a specific
year was recorded at the Amundsen-Scott Station: - 50°C, in 1976. Melting
occurs for a few days in summer, but the highest temperature recorded at the
South Pole is - 15°C. In Antarctica precipitation is estimated at 50 mm in the
Climates of the World Seen from an Ecotoxicological Perspective
27
interior plateau and 500mm along the coast. Most precipitation is due to cyclonic
storms: frost and rime also contribute to the accumulation. Insolation is
exceptionally great in summer, but the surface albedo is high and the snowy
environment limits the temperature rise.
The ground is snow covered much of the time. Accordingly there is little
convection and ventilation is poor in the absence of storms. Very strong
winds are produced orographically and by storms near the land-open water
margin during the winter season, with storm wind-speeds in excess of 50 knots
and gusts over 100 knots. Pronounced inversions that persist all day in valley
areas coupled with the incapacity of the cold air to hold significant quantities
of moisture result in locally intense concentrations of pollutants and ice-crystal
fogs.
The relative absence of precipitation scavenging and strong inversions have
been blamed for the net accumulation of pollutants, such as sulphates, mercury,
cadmium, vanadium, and manganese in the Arctic. The sources are temperatezone industrialized areas. The pollutants along with particles from other land
and oceanic sources, form an 'arctic haze', which is widespread and well mixed.
It is seasonal in concentration, the winter peak attaining levels that are 20 to
40 times greater than in summer. The haze is acidic, being about 30070sulphate,
but the levels of acidity are still ten times lower than in the industrialized areas
(Rahn and McCaffrey, 1979). This phenomenon is not reproduced in the
southern hemisphere.
ACKNOWLEDGEMENTS
The authors surveyed many literature sources in preparing this chapter.
Particular mention must be made of H.J. Critchfield's General Climatology
(1983), which was the source of many statistics. Critchfield's zonation concepts
closely conform to those of the authors, and his text is recommended for more
detailed information on zonal climates.
2.1.10
REFERENCES
Bruce, J. P. (1983). Climate and water quality. WMO Technical Conference on Climate
for Latin America and the Caribbean, Bogota. World Meteorological Organization,
Geneva.
Critchfield, H. J. (1983). General Climatology (4th edn.). Prentice-Hall Inc., Englewoods
Cliffs, N. J.
Koeppen, W., and Geiger, R. (1935). Handbuch der Klimatologie. Verlag von Gebriider
Borntraeger, Berlin.
Ottar, B. (1979). Long-range transport of air pollutants which are re-emitted to the
atmosphere by sublimation. In: Proceedings of WMO Symposium on Long-Range
Transport of Pollutants and its Relation to General Circulation induding Stratospheric/
Tropospheric
Exchange
Processes,
pp. 125a-125b. World Meteorological Organization,
Geneva.
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Ecotoxicology and Climate
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